Stearic acid
From Wikipedia, the free encyclopedia
| Stearic acid | |
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| Chemical name | Octadecanoic acid |
| Other names | Stearic acid |
| Chemical formula | CH3(CH2)16COOH |
| Molar mass | 284.47 g/mol |
| CAS number | [57-11-4] |
| Density | 0.847 g/cm3 at 70 °C |
| Melting point | 69.6 °C |
| Boiling point | 383 °C |
| Freezing point | 49.5 °C |
| Acid value | 200-210 mg KOH/g |
| Disclaimer and references | |
Stearic acid (IUPAC systematic name: octadecanoic acid) is one of the useful types of saturated fatty acids that comes from many animal and vegetable fats and oils. It is a waxy solid, and its chemical formula is CH3(CH2)16COOH. Its name comes from the Greek word stéar (genitive: stéatos), which means tallow. The term stearate is applied to the salts and esters of stearic acid.
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[edit] Production
Stearic acid is prepared by treating animal fat with water at a high pressure and temperature, leading to the hydrolysis of triglycerides. It can also be obtained from the hydrogenation of some unsaturated vegetable oils. Common stearic acid is actually a mix of stearic acid and palmitic acid, although purified stearic acid is available separately.
[edit] Uses
Stearic acid is useful as an ingredient in making candles, soaps, plastics, oil pastels and cosmetics, and for softening rubber. Stearic acid is used to harden soaps, particularly those made with vegetable oil.
Stearic acid is also used as a parting compound when making plaster castings from a plaster piece mold or waste mold and when making the mold from a shellacked clay original. In this use, powdered stearic acid is dissolved in water and the solution is brushed onto the surface to be parted after casting.
Esters of stearic acid with ethylene glycol, glycol stearate and glycol distearate are used to produce a pearly effect in shampoos, soaps, and other cosmetic products. They are addded to the product in molten form and allowed to crystalize under controlled conditions.
In fireworks, stearic acid is often used to coat metal powders such as Aluminium and Iron. This prevents oxidation allowing compositions to be stored for longer.
[edit] Reactions
Stearic acid undergoes the typical reactions of unsaturated carboxylic acids, notably reduction to stearyl alcohol, and esterification with a range of alcohols.
[edit] Metabolism
An isotope labeling study in humans[1] concluded that the fraction of dietary stearic acid oxidatively desaturated to oleic acid was 2.4 times higher than the fraction of palmitic acid analogously converted to palmitoleic acid. Also, stearic acid was less likely to be incorporated into cholesterol esters. These findings may indicate that stearic acid is less unhealthy than other saturated fatty acids.
[edit] See also
[edit] References
- ^ Emken, Edward A. (1994). "Metabolism of dietary stearic acid relative to other fatty acids in human subjects" (PDF). American Journal of Clinical Nutrition 60: 1023S–1028S. Retrieved on 2006-08-07.
- Merck Index, 11th Edition, 8761.
